Television system



g. 13, 1940. L. MAGUIRE TELEVISION SYSTEM Filed Nov. 16, 1938 LB m PC A!A2 A1 0PA SGI SSheets-Sheet 1 S65 VR INVE N TOR IL. MAGUIRE BY 6 aATTYS.

TELEVISION 5 15mm Filed Nbv.' 16, 1938 4 gs Sheeits-Sheet 2 INVENTOR 8IL. MAeulRE v ys A g- 13, 1940- 1.. MAGUIRE I 2,211,066

TELEVISION SYSTEM Filed Nov. 16, 1938 3 Sheets-Sheet 3 INVENTORI.L.MAGL)|RE 'ATTYS,

Patented Aug. 13, 1940 UNITED STAES PATENT OFFICE TELEVHSION SYSTEMIrwin Leonard Maguire, Elwood, Victoria,

Australia '7 Claims,

This invention relates to cathode ray and mechanical methods of scanningin television systems, and it has been devised to simplify difficultieswhich arise in photocell response, ampli- 5 fiers and the like in bothtransmission and reception. In particular the present invention providesfor reduction of transmission frequency with increased degree ofdefinition of a facsimile to thereby simplify diiliculties oftransmission reception and amplification of signals.

According to present day practice, for photocells other than the mosaictype, the light emitted by each picture point actuates thephotocellduring the time taken for a scanning spot to traverse one of said pointsand the response of gas filled types of photocell to this light isproportional to the time during which the light is incident upon it.Thus the greater the definition of the picture, the smaller is theresponse of the photocell for a given brilliance of the individualpicture points. Further, the picture points of the facsimile arerecreated during the time taken to scan corresponding points of thepicture and the apparent brightness to the eye of the recreated picturepoints of the facsimile depends, for a given source of light, upon thetime taken for the scanning spot to traverse the picture point. Further,the photocell response depends upon the total amount of light fluxemitted by the scanning spot and since the light of the scanning spotutilised for the recreation of the picture points of the facsimile ismore or less uniform and of a size equivalent to that of a picturepoint, it follows that no definite detail 35, of the picture orfacsimile which is smaller in.

size than a scanning spot, can be recreated. The

frequency of the video signal is proportional to the ratio of the areaof the picture frame to the area of the scanning spot and to the numberof picture frames scanned in a given time and thus the frequency of thevideo signal is proportional to the definition of the picture and thegreater the definition the higher the video signal frequency.

4 The present invention has for its objects the improvement ofdefinition in the facsimile reconstructed at the receiver and reductionof the video signal frequency, and according to this invention the firstmentioned object is attained by modulation of the light for the creationof facsimiles by means of a signal which is derived from the diiferencein effects of two similar signals subject to be transmitted which aresuccessively scanned in serial order. By this means the definition ofthe facsimile is rendered independent of the video signal frequency withresultant increase in the definition of the facsimile. 5

Reduction of transmission frequency is attained by a scanning methodcomprising the successive scanning of zones of the subject to betransmitted, said zones being equivalently proportioned and dimensionedto comprise a group of picture points whereby the individual picturepoints recreated in the facsimile at the receivermay be appreciablysmaller in area than the zones scanned at the transmitter. The relativedimensions of said group of picture points and individual picture pointsare determined by the size of the zone scanned at the transmitter andthe difierence in phase provided and utilized as above described at thereceiver.

Preferably the dimensions of each zone above- A mentioned areequivalently proportioned to a to single line of the picture frame atthe transmitter.

In the scanning operationatthe transmitter each picture point within azone of scanning is presented to the photo-cell for a period of timeequivalent to that occupied in the scanning of the complete zone, andthus the response of the photocell per picture point is increased. Thisadvantage is obtained by progressively revealing each zone to thephotocell until maximum disclosure is reached, following which the zoneis progressively concealed to zero before commencement of the scanningof the next zone.

The scanning of the picture may be efiected by known means such as acathode ray beam focussed on a photosensitive mosaic, but the image ofthe beam in lieu of being a spot is a zone or rectangular shaped areaequivalent in proportions to a line of the picture, and in scanning, thebeam image is caused to traverse the picture frame along the lines ofthe picture so as first to progressively reveal the picture points andthen to progressively conceal said points.

Alternatively in lieu of the image of the cathode ray beam beingfocussed to a zone of the proportions of a line of the picture, theimage of the cathode ray beam may be focussed to a spot as usual and thebeam oscillated at high frequency to cause the spot to traversebackwardsand forwards along a line and by superimposing a suitable sweepmovement to this oscillatory movement of the cathode ray beam thescanning zone produced by the oscillatory movement of the spot is causedto advance across the picture frame in the same manner and with the sameequivalent effect as when the cathode ray beam image was focussed to aline and the line was caused to advance across the picture frame andfurther, this scanning zone so produced by the oscillatory movement ofthe spot can be caused to fly back quickly as in known methods of spotscanning with cathode ray tubes.

Alternatively a scanning disc may be employed in which a series ofarcuate slots is arranged, said slots preferably being equivalentlyproportioned to a line of picture frame and angularly spaced so thateach slot progressively reveals a line of the picture to a photocell andthen progressively conceals the line from the photocell before the nextsucceeeding slot commences to reveal the next succeeding line zone.

The method of integrating and differentiating the effects obtained inscanning by the methods of this invention will be understood from thefollowing analysis:

Assume that there are 11 picture points per zone of the picture, andassume for identification purposes that the points are numbered I, 2, 3,etc. starting from the end of the zone when the first picture point isdisclosed to the photocell. Assume that the time taken to fully disclosethe zone is nt seconds and that the time taken to traverse a picturepoint from one end of the picture point to the other is seconds. Assumethat the light flux emitted by the picture points I, 2, 3, etc. in tseconds is W1, W2, W3, etc. respectively. The amplitude of the photocellcurrents at any instant is proportional to the light which is incidentat this instant upon the cell so that at the respective instants thatthe number of picture points I or 2 or 3 etc. are simultaneouslydisclosed, the amplitude of the photocell currents is proportional toetc. respectively.

The suppositional graph marked Fig. 1 in the drawings accompanying thisspecification shows the variations in amplitude of the photocell currentwith time of scanning a zone of the picture. The abscissae shows thenumber of picture point revealed at any instant, and the ordinates showamplitude of the photocell current when the zone discloses I or 2 or 3or more eto., picture points to the photocell.

The video signal current is equivalent to the photocell currents and theamplitude of the photocell currents and the video signal currents at anyinstant is thus proportional to the integrated eifect of the picturepoints which at that instant are incident upon the photocell.

At the receiver the effects of the video signal are differentiated toobtain an effect which is proportional to the rate of change inamplitude of the video signal. This instantaneous rate of change inamplitude of the video signal corresponds to the change in amplitude ofthe photocell currents due to the disclosure at that instant of apicture point to the photocell. Thus the effects so obtained correspondto the individual effects of the picture points disclosed to thephotocell. When these effects are utilised for the modulation of thelight at the receiver they enable the picture points of the facsimile tobe recreated.

Referring to the drawings accompanying this specification, Fig. 1 aspreviously mentioned is a graph showing variations in amplitude ofphotocell current with time of scanning a picture zone.

Fig. 2 shows a circuit arrangement for transmitter and receiverequipment organised to incorporate an embodiment of the invention inwhich scanning operations are performed by a cathode ray method.

Fig. 3 shows a mechanical scanning disc devised for use at a transmittershown diagrammatically in Fig. 4, While Figs. 5 and 6 are views, similarto Figs. 3 and 4, of a modified mechanical scanning arrangement.

Fig. '7 is a schematic lay-out of a cathode ray tube arranged foroptical creation of facsimiles Within the scope of the presentinvention.

Fig. 8 is a diagrammatic representation of the operation of the triplebeam produced by the cathode ray tube shown in Fig. 7.

Fig. 9 is a graph showing two curves plotted in the manner of the curvein Fig. l and illustrating difference in amplitude of duplicate signalsdiffering in phase relationship.

Figs. 10, 11, 12 and 13 are circuit diagrams illustrating differentnetworks for obtaining phase differences between duplicate signals.

As before stated the essential characteristic of the invention residesin utilizing the difference in effects of two similar signals, whichdiffer in phase and are generated from a single video signal produced atthe transmitter, to modulate the light used for creating facsimiles atthe receiver, and consequently it will be convenient first to refer tothe group of figures of drawings marked Figs. 10 to 13 inclusiveillustrating phasing methods.

In each figure of the group (Figs. 10 to 13) the received single videosignal is applied at VS being the input terminals of the network, onebranch Bl consisting of a potential dividing resistance VR and thesecond branch 132 which may be arranged as a constant impedancecomprising resistance and capacity and inductance at SR, SC, and Sirespectively, or it may be arranged as a reactance comprising a capacityand resistance SC and SR respectively.

In Figs. 10 and 12 the output from branch B2 is taken from the capacityleg and in Figs. 11 and 13 from the inductance leg.

The arrangements shown in Figs. 10 to 13 each provide a duplicate of thevideo signal in each of the branches Bl, B2 and by adjustment of thecapacity and/or inductance in the latter branch the current therein canbe caused to lead or lag behind that in branch Bl to set up the requiredphase difference at the output terminals at OS, which terminals bearsimilar reference characters in Fig. 2 and are connected to theamplifier at RAZ in that figure. Resistance VR may convenientlyconstitute the grid leak resistance of the input tube of amplifier RA2.

Referring now to Fig. 2, the subject to be televised is indicated as atravelling film at TF and is scanned by the cathode ray generated bycathode ray tube CR.

Reduction of video signal frequency in accordance with the invention andto obtain the ad vantages of low frequency transmission is attained byso scanning zones successively, each zone being equivalent to a line ofthe subject, that each zone is progressively revealed to the photocelluntil maximum disclosure is reached following which the zone isprogressively concealed to zero before scanning commences of the nextsucceeding zone. By this method the amplitude of the photocell currentsat any instant is equivalent to the sum of the picture points revealedto the photocell at the same instant.

Scanning means for carrying out the scanning method stated may consistof conventional cathode ray tube apparatus or mechanical scanningdevices such as a Nipkow type of disc having its scanning aperturesdimensioned as hereinafter described.

In utilizing cathode ray scanning means, the image of the beam isfocussed to a rectangular area equivalent in proportions to one line ofthe subject and the beam is caused to sweep along the line toprogressively reveal and conceal the line as before stated. In lieu offocussing the said image of the beam to a rectangular area, it may befocussed to a spot as usual and the beam oscillated at high frequencyalong a path equivalent to a line of the subject and a sweep movement isimparted to said path to eifect said progressive revealment andconcealment.

Referring now in detail to Fig. 2, thescarming at the transmitter isperformed by the cathode ray methods above described by the cathode raytube OR, the resultant beams being directed by a lens L to the photocellat PC. The photocell currents are led to the coupled ampliflerunits atAl and A2 thence to modulator unit at M where the output current fromthe latter is superimposed upon a carrier frequency and the modulatedcarrier frequency is applied to the transmitting aerial at TA viaoscillator-power amplifier OPA. The line sweep oscillator is indicatedat LG and the line sweep-synchronising signal generator at SGI and theseare connected to the deflecting plates at LD of the cathode ray tube CR,while the frame deflecting plates FD of the latter are connected to'theframe sweep-synchronising signal generator 8G2.

At the receiver the pick-up at RA of the incoming low frequency impulsesfrom TA are received and amplified at RA! and then applied to a phasingnetwork (comprising branches BI and B2) for the purposes previouslydescribed and as ascertained by reference to Figs. 10 to 13 inclu sive.

The output from the phasing network terminals OS is applied to theamplifier RA2 and thence to the cathode ray modulating electrode of thecathode ray tube at CRl. The line sweep potentials are applied to thedeflecting plates at LDI and the frame sweep potential to thedeflectingplates at FDl, The synchronising signals are applied from RA!to 8G3 and SGQ.

Referring to Figs. 3 to 6 inclusive depicting means for mechanicalscanning as an alternative to the cathode ray tube scanning methodsdescribed, in Fig. 3 is shown a scanning-disc SD having scanningapertures SDI, arranged in a single spiral path. Each of said scanningapertures SD! is proportioned so as to be equivalent in shape to oneline of the picture frame and said apertures are spaced apart adistance. at least equivalent to the length of said line. The scanningdisc SD is shownin Fig. i asso ciated with its related photocell PC andsubject at S.

In Fig. 5, showing an alternative arrangement of the scanning aperturesSDI in Fig. 3, the scanning apertures are disposed in a circular path inthe scanning disc SD for scanning a continuously travelling film TF asshown in Fig. 6 in juxtaposition with an associated photocell PC andlight source at US.

Reference will now be made to Figs. '7 and 8 for the purpose of furtherdescribing the alter native arrangement for creation of facsimiles atthe receiver in which the phasing effect beforementioned is provided byutilizing a cathode ray tube providing a diiferentially illuminated zoneequivalent to a line of the picture frame.

Referring particularly to Fig. 8 three illuminated zones are indicatedat Z, Zl, and Z2, one of said zones Z! being assumed as illuminated todouble the brilliance of each of the zones Z and Z2.

The zones Z, Zl, Z2 are superimposed with overlap as'indicated generallyat Z and, so related, are swept across the picture frame PF to effectthe progressive revealment and conceal=- ment of a line of pictureframe.

Fig. 7 depicts a cathode ray tube CR2 arranged to create the zones Z,Zl, Z2 related and functioning as above described.

The tube CR2 is shown provided with three electron guns EG directedtowards a common focal point on the screen at CS. The rays EG! emanatingfrom the guns EG are oscillated at high frequency by the deflectingplates LS to illuminate superimposed overlapped zones equivalent to Z,.Zl, Z2 on the screen at CS. The deflecting plates at LS also effect theline sweep motion and deflecting plates FS effect the frame sweep motionof the zone Z0. The deflecting plates EG2 are utilized to relativelylocate the overlapped zones Z, Z! and Zii.

From the foregoing it will be evident that if three zones are relativelyilluminated as above set forth and the light of the brightest zone Z ispositively modulated whilst the light of each of zones Z, Z2 isnegatively modulated (i. e. the light of the zone Zl is modulated toincrease in brightness, while the light of the zones Z, Z2 is modulatedfor decrease in brilliance) and if said 7 1 the zones becomesdifferentiated due to the effects of persistance of vision so that themind is ren dered conscious of the creation of the picture points I, 2,3 etc. If the zones are scanned and located at the receiver in a mannercorresponding to the scanning of the zones at the transmitter thena'facsimile will be created.

At the receiver differentiation of the effects of the video signal maybe obtained electrically or optically.

Assume that it is desired to effect the differ entiation electrically.

The amplitude of the video signals, up to the time of disclosing thezone at the transmitter to its maximum extent to the photocell, at the 7of this network the current lags behind that of the other branch by thetime taken to scan a picture point, thus at the time of scanning thepicture points 1,2, 3, '4 etc. the currents in one branch haveamplitudes proportional to W1 (Wi-I-W2), (VVI+W2+VV3),(VVl-l-VVz-PWH-Wc) etc., and at the time corresponding to these valuesof currents the amplitude of the currents flowing in the other branchare 0, W1, (W 1+W2), (W1+ W2+W3)+etc. 'The instantaneous difference inpotential between the potentials across these branches at the time ofscanning picture points I, 2, 3, 4, etc. is thus proportional to:Wi=0=W1, (Wi+W2)(W1)=W2; (W1+W2+ W3) (W1+W2) :Ws; (W1+W2+Ws+W4)(WI+W2+W3) =W4 etc.

These results are illustrated by the difference in amplitude of the twocurves marked A and B in the graph shown in Fig. 9 of the accompanyingdrawings. These curves are plotted according to the assumptions made forplotting the graph shown in Fig. 1. Curves A and B are identical but areplotted so as to be out of phase by one picture point. The top row offigures along the abscissa corresponds to the total number of picturepoints simultaneously disclosed for curve A and correspondingly thebottom row of figures along the abscissa applies to curve B of thecurves shown in Fig. 9. Each curve is hereinafter called the modulatingsignal.

The amplitude of the modulating signal, obtained by taking thedifference in potential of the currents flowing in the two branches ofthe network at the time of scanning the picture points I, 2, 3 etc., isthus proportional to W1, W2, W3 etc. This signal is thus equivalent tothe signal generated by scanning the picture point by point inaccordance with the usual method of picture scanning at the presenttime. Thus, if a known type of scanning device such as the oathode raytube is used as a receiver and its beam is modulated by the modulatingsignal and the focussed spot of the cathode ray is moved to correspondwith the movements of the scanning zone at the transmitter and so thatthe focussed spot at the receiver corresponds in location with theleading end of the scanning zone at the transmitter then the facsimilewill be created to correspond with the picture scanned at thetransmitter.

Assume that it is desired to effect the differentiation optically.

At the receiver an area, equivalent in proportions to the correspondingzone at the transmitter, is uniformly illuminated by a modulated lightWhose brilliance is proportional to the amplitude of the photocellcurrents. Assume that this illuminated zone at the receiver is revealedto the eye of an observer in a manner corresponding to the revealment ofthe picture zones at the transmitter, i. e. at instants corresponding tothe revealment of respective picture points I, 2, 3, etc. there arerevealed to the observer at the receiver corresponding respective zonepoints I, 2, 3, etc. The effect upon the eye, of the light emitted atpoints I, 2, 3 etc., is that due to persistance of vision and thebrilliance of the points of the zone appears to the eye as beingproportional to the total flux revealed per picture point of the zoneduring the time that the zone is scanned or revealed to its maximumextent.

Assume that the total light flux emitted by the points of the zone atthe receiver during the time that the zone is revealed to the eye is I,2, 3, etc. where +(W1+W2+ +Wn) etc., and as explained previously thebrightness of the points I, 2, 3 of which the mind is renderedconscious, is proportional to the total flux emitted and thus (1), (2),(3) is the apparent brightness of the picture points I, 2, 3, etc.

Inspection of formulas for (1), (2), (3), tc, shows that the variousquantities W1, W2, W3 etc., representing the brightness of theindividual picture points may be determined, thus:

1= 2= 1=( (3)( W 3) (4) (W W )-(3 (4) (z f df and so on and for Wn-1 weget Wn1=2 (n 1) -(n) (n2) Corresponding formula to the foregoing can beobtained if the mode of Scanning is reversed i. e. the zone first fullyprogressively reveals the picture points to the photocell or the viewingscreen and these picture points are then progressively concealed.

From these formula it is apparent that if three zones are uniformlyilluminated so that one zone is twice as bright as the illumination ofeither of the other two zones and if these latter zones are illuminatedto the same degree of brightness and if the light of the brightest zoneis positively modulated whilst the light of the other zones isnegatively modulated i. e. when the light of the brightest zone ismodulated so as to increase in brightness, the light of the other twozones is modulated so as to decrease in brilliance, and if the images ofthe zones are superimposed so that the first disclosed picture point ofeach of the zones is a picture point out of phase in the order shown bythe formula for W1, W2, W3 etc., then the light of the zones becomesdifferentiated due to the effects of persistence of vision so that themind is rendered conscious of the creation of the picture points I, 2, 3etc. If the zones are scanned and located at the receiver in a mannercoresponding to the scanning of the zone at the transmitter then thefacsimile will be created.

I claim:

1. In a television system, the method consisting of progressively andcontinuously scanning, in seriatum, individual zones of the subject tobe transmitted, completing the scanning of one zone before commencing toscan the next zone of the series, converting the light effects from eachzone into an equivalent electric signal, amplifying the latter, applyingthe amplified signal to a carrier frequency which is transmitted to areceiver,

amplifying the received video signal, multiplying the latter with aphase difference between the multiple signals, and converting saidlatter signals, simultaneously in a common zone, into equivalentsuperimposed and overlapped fluorescently visible signals, whereby thebeforementioned phase difference creates an optical eifect corespondingwith the light values constituting the elementary picture points presentin each zone scanned at the transmitter.

2. In a television system, the method consisting of progressively andcontinuously scanning, in seriatum, individual zones of the subject tobe transmitted, completing the scanning of one zone before commencing toscan the next zone of the series, converting the light effects from eachzone into an equivalent electric signal, amplifying the latter andapplying the amplified signal to a carrier frequency which istransmitted to a receiver, amplifying the received video signal,duplicating the latter with a phase diflerence between the duplicatesignals, and applying the potential of a signal due to said phasedifference to modulate light used for the creation of a facsimile of thesubjecttransmitted, whereby an optical effect is created correspondingwith the light values constituting the elementary picture points presentin each zone scanned at the trans- I mitter.

3. In a television system, a transmitter comprising scanning means forcontinuously scanning, 'in seriatum, individual zones of the subject tobe transmitted and completing the scanning of one zone before commencingthe scanning of the next zone of the series, a photo-electric cell,means for applying the light effects from each of said zones to thephoto-electric cell, means for amplifying the output from thephotoelectric cell, means for applying the amplified signal to atransmissible carrier frequency, a receiver for said amplified signalcomprising means for amplifying and means for multiplying the receivedsignal, means for creating a phase difference between the multiplesignals, means for simultaneously converting said multipledifferentially phased signals into equivalent superimposed visiblesignals, and means for locating the latter signals in a common zone,whereby the beforementioned phase difference creates an optical effectcorresponding with the light values constituting the elementary picturepoints present in each zone scanned at the transmitter.

4. A television system, consisting of a transmitter comprising scanningmeans for continuously scanning, in seriatum, individual zones of thesubject to be transmitted and completing the scanning of one zone beforecommencing the scanning of the next zone of the series, a photoelectriccell, means for applying the light effects from each of said zones tothe photo-electric cell, means for amplifying the output from thephotoelectric cell, means for applying the amplified signal to atransmissible carrier frequency, a receiver for said amplified signalcomprising means for amplifying and means for duplicating the receivedsignal, means for creating a phase difference between the duplicatesignals, and means for applying the potential of a signal due to saidphase difference to modulate light used for the creation of a facsimileof the subject transmitted, whereby an optical effect is createdcorresponding with the light values constituting the elementary picturepoints present in each zone scanned at the transmitter.

5. A television system, consisting of a transmitter comprising scanningfor continuously scanning, in seriatum, individual zones of the subjectto be transmitted, a photo-electric cell, means for applying the lighteffects from each of said zones to the photo-electric cell, means foramplifying the output from the photo-electric cell, means for applyingthe amplified signal to a transmissible carrier frequency, a receiverfor said amplified signal comprising means for amplifying and means forduplicating the received signal, and means for creatinga phasedifference between the duplicate signals, consisting of a phasingnetwork constituted of two branches connected to the amplified output ofthe receiver, one of said branches comprising a potential dividingresistance and the other of said branches comprising a constantimpedance or reactance, the output potential from said phasing networkbeing applied to modulate light used for the creation of a facsimile ofthe subject transmitted, whereby an optical effect is createdcorresponding with the light values constituting the elementary picturepoints present in each zone scanned at the transmitter.

6. A television system, consisting of a transmitter comprising scanningmeans for continuously scanning, in seriatum, individual zones of thesubject to be transmitted, a photo-electric cell, means for applying thelight effects from each -of said zones to the photo-electric cell, meansfor amplifying the output from the photoelectric cell, means forapplying the amplified signal to a transmissible carrier frequency, areceiver for said amplified signal comprising means for amplifying andmeans for duplicating the received signal, means for creating a phasedifference between the duplicate signals, consisting of a phasingnetwork constituted of two branches connected to the amplified output ofthe receiver, one of said branches comprising a potential dividingresistance and the other of said branches comprising a constantimpedance or reactance, a cathode ray tube, ray deflecting plates insaid tube, means for amplifying the output from said phasing network,means for applying said amplified output potential to modulate the raygenerated by said cathode ray tube, and means for applying frame sweepand line sweep potentials to said ray deflecting plates, whereby anoptical effect is created corresponding with the light valuesconstituting the elementary picture points present in each zone scannedat the transmitter.

7. In a television system, a transmitter comprising scanning means forcontinuously scanning, in seriatum, individual zones of the subject tobe transmitted, a photo-electric cell, means for applying the lighteffects from each of said zones to the photo-electric cell, means foramplifying the output from the photo-electric cell, means for applyingthe amplified signal to a transmissible carrier frequency, a receiverfor said amplified signal comprising means for amplifying and means formultiplying the received signal, consisting of a cathode ray tubecomprising ray generating electrodes to each of which the receivedamplified signal is simultaneously applied to modulate said rays, meansfor deflecting said modulated rays to impart overlap or phase shiftthereto, and means for applying frame sweep and line sweep to saiddeflected rays, whereby an optical effect is created corresponding withthe light values constituting the elementary picture points present ineach zone scanned at the transmitter.

Y IRWIN LEONARD MAGUIRE.

